Tom Cruise suffers the effects of an alien war as well as about an hour of exposition in Oblivion, a science-fiction movie with a not-terrible concept that is unevenly executed.

You know how, in school, you’d have all these big plans about that report, how you were going to include charts and graphs and extensive footnotes as well as hand-drawn illustrations and a plastic cover? And then remember how, in the end, what you turned in was about two pages of iffy reasoning stretched to fill six with extensive block quotes and bigger font? That’s Oblivion — bigger font and so much padding.

Jack Harper (Cruise) is living in what looks like a very retro-modern apartment in Star Wars’ Cloud City. Actually, it’s some sort of outpost on a ruined Earth where he and teammate Victoria (Andrea Riseborough) are working to keep water collection stations and the drones protecting them running. See, here in 2077, the Earth is essentially uninhabitable, after nuclear war with an invading force of aliens led to contamination of most of the planet. The population has been sent to Saturn’s moon Titan, and now a small crew is left to make sure the water collection (the sea waters will help make fusion energy for Titan, or something) goes smoothly. Apparently, a remnant of the invading alien force is still alive on Earth and causing insurgency-like trouble.

Though the glass apartment in the cloud has all the comforts, including a glass-bottom pool and a lovey-dovey Victoria, Jack longs for something more. Even though the invasion happened 60 years ago, before the Tom-Cruise-aged Jack was born, he has dreams at night about a woman and a bustling New York City. WALL-E-style, he picks up artifacts of life on Earth — a baseball cap, books, a bobblehead. He even takes some of these to a lush, hidden valley, where he has built himself a small solar-powered house by a lake. Even though he knows life is waiting for him on Titan, he can’t shake the feeling that Earth is where he belongs.

But then, a spacecraft — a NASA craft that is, as he says, “pre-war” — crashes containing Julia (Olga Kurylenko), a woman who looks very familiar. Suddenly, Jack is not so sure that life on Earth is not exactly as he was told.

See how I got through the entire description without getting to Morgan Freeman? Yes, he is in the movie, in a fairly crucial role, but he and his plot twists do not show up until about an hour in (this is also when Nikolaj Coster-Waldau, a.k.a. Jamie Lannister, shows up). His first scene is built up, with camera shots and atmospherics, to be a Big Deal, a movie game-changer. (My 13-year-old stepson gave his review of the movie saying, essentially, that the first half was boring but then Morgan Freeman showed up and it got better.) But I felt like the words “actual dialogue to come later” were stamped on these pages of the script. It’s like receiving a dessert that is just a plate of drizzled chocolate sauce, mint leaves and a sliced strawberry. You get that something important is supposed to go there but you are missing the cake.

This might be a problem of too much — too much plot crammed into the final 40 minutes or so of this movie, where the first hour-plus was filled with lovely futuristic sets, snazzy clothes (would future tech workers really wear four-inch stilettos, as Victoria does?) and a mopey Jack, sneaking off to his lake hideaway to put on a flannel shirt and listen to records. There are, at any moment, a lot of ways this movie could go. Rather than narrowing to a point, the story seems to metastasize out, with details upon details suggesting a variety of things that could happen, could have happened or could maybe be happening right now. It’s like a self-generating choose-your-own adventure book.

That said, this tilted frame of a movie is interesting. It has elements of 2001: A Space Odyssey and Moon and nice juicy bits to chew on after you leave the theater. (Such as: OK, stilettos aren’t so crazy, maybe, if you essentially work from home and spend most of your day sitting, as Victoria does running the computer back-up systems while Jack scouts around on Earth, but would you really wear a sheath dress and an unforgiving metal belt? While sitting?) Tom Cruise is a good journeyman action star — he shows up on time, hits his marks and doesn’t get in the way of the movie. Meanwhile, for me, the standout is Riseborough, who actually does a good job of being — without being too spoilery — questionable. She has an Emily Blunt category that works very well with the part.

Maybe the secret is to look at Oblivion itself as a placeholder — a not bad, not good little hold-over until the real sci-fi blockbusters show up in a few weeks. C+

Rated PG-13 for science-fiction action violence, brief strong language and some sensuality/nudity. Directed by Joseph Kosinski with a screenplay by Kosinski, Karl Gajdusek and Michael Arndt (from a comic book by Kosinski and Arvid Nelson), Oblivion is two hours and five minutes long and distributed by Universal Pictures.